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What is 1 + 3?
Provides protection and sometimes support
single-layered epidermis, sometimes with cuticle
cuticle, epidermis, connective tissue (dermis), layer of iridocytes, and more connective tissue
epidermis (hypodermis) that secretes a complex cuticle, inner procuticle (protein and chitin) and outer epicuticle (protein and lipid for waterproofing)
flexible or calcified or sclerotized: often serving as an exoskeleton
Must be shed to allow growth
have epidermis (stratified epithelium of ectodermal origin) and dermis (connective tissue of mesodermal origin)
Epidermis keratinized in terrestrial forms (scales, feathers, hair)
armor —> flexible scales) (antlers
structural (physical structure affects light) or pigment based (chromatophores)
crystals of g or p
Melanins, carotenoids in xanthophores), iridophores